Azithromycin !

A macrolide that lingers for days in the tissues, so short courses work. Used for atypical pneumonia, chlamydia, trachoma and cholera.

Updated 2026-11-01

Class: Macrolides
Target: Bacterial ribosome, 50S subunit (23S rRNA, exit tunnel)
ATC code: J01FA10
WHO Model List of Essential Medicines

Bacterial ribosome, 50S subunit (23S rRNA, exit tunnel)Azithromycin

The figure shows azithromycin bound in the exit tunnel of the 70S ribosome of Thermus thermophilus, a model bacterium.

Target in 3D: Bacterial ribosome, 50S subunit (23S rRNA, exit tunnel). PDB structure 4V7Y (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Azithromycin binds the 23S rRNA of the 50S subunit and blocks the tunnel through which new proteins leave the ribosome; it also hinders assembly of the 50S subunit. Protein synthesis stops and the bacteria cannot grow. It is taken up by tissues and white blood cells and released slowly, so its levels in tissue stay high long after blood levels fall.

Enters tissues and phagocytes and builds up there
Binds the 23S rRNA in the 50S exit tunnel
The growing protein chain is blocked
Bacteria stop multiplying

Pharmacokinetics

Absorption: Oral bioavailability about 38%; tablets can be taken with or without food. Also given by slow IV infusion.
Distribution: Extensive uptake into tissues (lung, tonsil, cervix, prostate) and phagocytes.
Elimination: Mainly in the bile as unchanged drug.
Half-life: Terminal half-life about 68 hours, because of slow release from tissues.

Indications

Community-acquired pneumonia, including atypical bacteria (Mycoplasma, Chlamydophila, Legionella) Community-acquired pneumonia →
Urethritis and cervicitis due to Chlamydia trachomatis Chlamydia infection →
Gonococcal infection, given together with ceftriaxone (WHO list) Gonorrhoea →
Streptococcal pharyngitis when a β-lactam cannot be used Streptococcal pharyngitis →
WHO first-choice uses: trachoma, yaws, cholera and typhoid fever; chancroid

Adverse effects

Common

Diarrhoea, nausea and abdominal pain
Headache and dizziness
Pain or redness at the infusion site (IV form)

Contraindications

Known allergy to azithromycin, erythromycin or any macrolide or ketolide
Previous cholestatic jaundice or liver dysfunction with azithromycin

Key interactions

Warfarin: May increase its anticoagulant effect; prothrombin time is checked.
Nelfinavir: Raises azithromycin levels; liver enzymes and hearing are watched.
Other QT-prolonging drugs: Additive risk of arrhythmia.

What is monitored

ECG in patients with QT prolongation, low potassium or magnesium, or heart disease
Liver tests if symptoms of hepatitis appear
Stool pattern for C. difficile

Administration and safety

The IV form is given only as a slow infusion, never as a bolus or intramuscular injection
Too concentrated an infusion causes local vein reactions: follow the product's dilution instructions
Sound-alike names: azithromycin and erythromycin are different drugs

Nursing care

Ask about macrolide allergy and previous liver problems
Check the infusion site for pain and redness
Teach to report palpitations, fainting, yellow skin or severe diarrhoea
In young infants, ask the family to report vomiting or irritability with feeds

Pregnancy and breastfeeding

Available data have not shown a clear risk of major birth defects.

Test yourself

Think of the answer, then tap the question to see it.

Why can azithromycin be given in short courses?

It is taken up by tissues and phagocytes and released slowly, giving a terminal half-life of about three days.

Why does azithromycin have fewer interactions than clarithromycin?

It hardly inhibits CYP3A, while clarithromycin is a strong inhibitor.

Which cardiac effect is checked in a patient with long QT receiving azithromycin?

QT prolongation, which can lead to torsades de pointes.

How is azithromycin used for gonorrhoea on the WHO list?

Together with ceftriaxone, not alone.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - AZITHROMYCIN tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - AZITHROMYCIN MONOHYDRATE injection, powder, lyophilized, for solution (DailyMed (U.S. National Library of Medicine), 2026); Azithromycin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).

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Representative model, for educational purposes only.